Metalizing composition

ABSTRACT

Metalizing compositions containing gold alloy flakes for decorative and electronic applications.

United States Patent [72] Inventor Oliver A. Short Wilmington, Del.

[21] Appl. No. 11,868

[22] Filed Feb. 10, 1970 W M if [23] Diiiision of Ser. No. 731,604, May 23, 1968,

Pat. No. 3,539,114. 7

[45] Patented Oct. 26, 1971 [73] Assignee E. I. du Pont de Nemours Wilmington, Del.

[54] METALIZING COMPOSITION 2 Claims, No Drawings 52 us. c1 106/1, 117/123, 117/160, 117/227,252/514 [50] FieldofSearch 106/1; 252/514; 117 227, 123 B, 160

[5 6] References Cited UNITED STATES PATENTS 3,440,062 4/1969 Hoffman 106 1 3,440,182 4/1969 Hoffman 106 1x 3,480,566 11/1969 Hoffman 106/1x 3,484,284 12 1969 Datesetal.... 106/1x Primary ExaminerLorenzo B. Hayes Attorney-John J. Klocko, III

ABSTRACT: Metalizing compositions containing gold alloy flakes for decorative and electronic applications.

. METALIZING COMPOSITION CROSS-REFERENCE TO RELATED APPLICATIONS This is a division of Ser. No. 731,604, filed May 25, 1968 now U.S. Pat. No. 3,539,114.

BACKGROUND OF THE INVENTION Gold powder can be made by many precipitation reactions. For example, chemical reduction from acid solutions may be accomplished by the use of ferrous sulfate or oxalic acid; chemical reduction from alkaline solutions can be accomplished with hydrazine sulfate. In addition, many metals in powder form (e.g., zinc, aluminum or magnesium) will displace gold from its halide solution to produce a gold powder. The gold powder produced by these conventional techniques have nodular or irregular particle shape; none of these prior gold powders are characteristic of a flake or waferlike gold.

These nodular gold powders have been used for many years in preparing decorative gold paints as well as printed circuit inks. However, it was hoped that flake gold would produce better results than nodular gold since experience with silver has shown that flake silver produces a smoother, more lustrous, more continuous film than nodular silver. Also, the flake silvers are far easier to disperse in organic vehicles in the formation of paints and inks.

The successful process for manufacturing flake silver is to mill a precipitated silver powder for several days in a ball mill, utilizing a mill vehicle composed of soap and water. Application of this technique to the preparation of flake gold has been unsuccessful due to the formation of large lumps of gold. In addition, no polishing of the gold resulted. Therefore, there is a need for process of preparing flake-type gold so that metalizations containing same may be advantageously used in decorative gold paints and printed circuit inks.

SUMMARY OF THE INVENTION This invention relates to a process of preparing flake gold comprising milling a gold powder in a liquid system containing a liquid selected from the group consisting of hydrocarbons and chlorinated derivatives thereof, and 1-20 percent by weight of a fatty acid for a sufficient time to produce gold flakes wherein there is no significant formation of gold lumps.

In addition, metalizing compositions comprising the gold flake are produced for decorative and electronic applications.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred process of preparing flake gold comprising milling a gold powder, which is a gold/mercury alloy containing l-l percent by weight mercury, in a liquid system which consists essentially of (a) a liquid selected from the group consisting of aromatic hydrocarbons,acyclic hydrocarbons and chlorinated derivatives thereof, and (b) 1-20 percent of a saturated fatty acid, and 0-1 percent finely divided rhodium dispersed in said liquid system, for a sufficient time to produce gold flakes wherein there is no significant formation of gold lumps.

One of the most important aspects of this invention resides in the discovery that a fatty acid acts as a wetting agent, to coat the gold particles and prevent the particles from agglomerating. Various saturated and unsaturated fatty acids may be used; these include butyric acid, caproic acid, lauric acid, stearic acid, behenic acid, cerotic acid, oleic acid, linoleic acid, parinaric acid and erucic acid. The fatty acid should comprise 1-2 percent by weight of the liquid system to prevent the gold particles from agglomerating.

The milling may be carried out by any appropriate procedures which are well known to those skilled in the art. However, it has been found that glass beads produce gold flakes with very smooth surfaces. Glass beads provide a polishing action rather than a grinding action that would be produced by other common milling techniques, such as by porcelain milling.

The liquid system which is used as the milling medium must contain a liquid in which the fatty acid will dissolve. The function of the solvent is to dissolve the fatty acid so that the acid is molecularly distributed throughout the liquid system thereby permitting the acid to coat the gold particles. Many of the common organic solvents can be used for this purpose. In particular, aromatic hydrocarbons, acyclic hydrocarbons and their chlorinated derivatives may be used so long as the fatty acid is soluble in the liquid hydrocarbon or chlorinated derivative. Typical solvents include: xylene, toulene, benzene and trichlorethylene.

The term a gold powder" is intended to include a metallic gold in physical or chemical combination with various other compatible metals. Mixtures of gold and other precious metals, alloys of gold and other metals, and various other combinations of other metals withgold are within the scope of this technology. A preferred goldpowder is a gold/mercury alloy containing 1-l0 percent by weight of mercury. It has been found that the alloying or mercury in the gold powder produces a gold flake that is harder, less malleable and does not contain lumps. Other metals such as platinum, palladium or silver may also be used in combination with the gold.

In another preferred aspect of this invention, small amounts of rhodium may be dispersed in the liquid system. Generally, O-l percent by weight of finely divided rhodium may be included in the liquid system to provide a harder and brighter polished gold flake.

The process should be carried out for a sufficient time to provide gold flakes which are hard, highly polished and do not contain any significant amount of lumps. In general a suffcient milling time has been found to range from 8-100 hours. A preferred laboratory operating time is considered to be from 60-70 hours.

EXAMPLE 1 A gold/mercury alloy powder containing approximately 5 percent mercury was prepared as follows: A gold chloride solution was prepared by dissolving 1,200 g. of metallic gold in aqua regia.

To the AuCI, solution was added l.5 gal. water and 84 g. HgCl this mixture was stirred until the HgCl crystals dissolved. Then 3 gal. of dilute NH OH was stirred into the AuCl /HgCl solution to produce a uniform slurry. Finally, an excess of dihydrazine sulfate, which had previously been dissolved in water, was added with constant agitation to the slurry. Finely divided modular gold/mercury alloy powder was allowed to precipitate, separated from the slurry and then washed.

Into an 8 oz. glass jar with a screw lid, was placed 225 g. V.- inch glass beads, 50 g. of the finely divided gold/mercury alloy powder prepared above, 60 cc. of xylene and 3 g. stearic acid. The lid was secured on the jar,and the closed jar was rotated on a ball mill rack at r.p.m The milling operation was carried out for 65 hours. After this time the gold powder was filtered from the liquid system and washed. It was observed in the form of flake gold and displayed a bright appearance.

For purposes of further illustrating this invention the following examples, as tabulated in table I, are described. The same gold powder and procedures described in example 1 were utilized. A gold flake having a bright appearance was produced in all examples. I

TABLE 1 Examples 2 3 4 5 Gold Powder 50 50 50 200 Xylene 60 60 60 240 Stearic Acid 5 g. 10 g. 3 g. 20 g. Rhodium Powder 0 0.l g. 0160 g. Milling Time 65 hr 65 hr 65 hr 65 hr Mill Size 8 oz 8 02 l qt.

glass glass glass porcelain jar jar jar A metalizing composition was prepared from the gold flake of Example 4. The composition contained 95 percent flake gold and 5 percent of.a finely divided inorganic binder (65 percent PbO, 25 percent SiO and 10 percent B 0 dispersed in a vehicle consisting of 8 percent ethyl cellulose and 92 percent beta terpineol. This gold composition was printed in the form of electrodes on an alumina substrate and fired at 950 C. Highly conductive, electrodes resulted.

The fold flake of this invention can be used to prepare various metalizing compositions. In general, conductor compositions containing gold flake are more useful since a continuous gold film is desired in the ultimate fired structures. However, this does not limit the scope of the invention and the gold flake may also be used in various other metalizing compositions, such as resistor compositions. The metalizing compositions, which contain the gold flake may be dispersed in an inert vehicle. Additionally, metalizing compositions can also contain a finely divided inorganic binder (e.g., glass, bismuth oxide, cerium oxide, etc.); for example, l-99 percent by weight of the flake gold and 1-99 percent by weight of an inorganic binder may be dispersed in an inert vehicle. Any of the conventional components and proportions of ingredients may be included in the metalizing compositions of this invention. For example, see commonly assigned Hoffman, Ser. No. 506,986, filed Nov. 9, 1965 now U.S. Pat. No. 3,385,719; Short, U.S. Pat. No. 2,819,170, and Larsen et al., U.S. Pat. No. 2,822,279.

In preparing the metalizingc ompositions, itis desirable, although not necessary, to disperse the solids in a vehicle. Any inert liquid may be utilized as a vehicle. Water or any one of various organic liquids, with or without thickening and/or stabilizing, and/or other common additives may be used. Examples of organic liquids that can be used are the aliphatic alcohols; esters of such alcohols, for example, the acetates and propionates; the terpenes, such as pine oil, alphaand betaterpineol and the like; solutions of resin such as polymethacrylates of lower alcohols, or solutions of ethyl cellulose, and solvents such as pine oil and the monobutyl either of ethylene glycol monoacetate. The vehicles of my copending application, Ser. No. 617,855, filed Feb. 23, 1967, and expressly abandoned on Nov. 17, 1969 may also be used. The vehicle may contain or be composed of volatile liquids to promote fast setting after application; or it may contain waxes, thermoplastic resins or the like materials which are thermofluids so that the vehicle-containing composition may be applied at elevated temperatures to a relatively cold ceramic body upon which the composition sets immediately.

The proportions of inert vehicle: solids (flake gold, glass, etc.) in the metalizing compositions of this invention may vary considerably depending upon the manner in which the paint or paste is to be applied and the kind of vehicle used. Generally, from 30-90 percent solids are dispersed in from 70-10 percent by weight ofthe inert liquid vehicle.

Since it is obvious that many changes and modifications can be made in the above-described details without departing from the nature and spirit of this invention, it is to be understood that the invention is not to be limited to said details except as set forth in the appended claims.

I claim:

1. In a metalizing composition comprising metal, finely divided inorganic binder and an inert liquid vehicle, the improvement which comprises as the metal a gold flake produced by a rocess comprising milling a old powder, which is a gold mercury alloy containing 14% percent by weight mercury, in a liquid system which consists essentially of (a) a liquid selected from the group consisting of aromatic hydrocarbons, acyclic hydrocarbons and chlorinated derivatives thereof, and (b) l20 percent of a saturated fatty acid, and 0-1 percent finely divided rhodium dispersed in said liquid system.

2. A metalizing composition in accordance with claim 1 comprising 1-99 percent gold flake and 99-1 percent of a finely divided inorganic binder.

* i i i 

2. A metalizing composition in accordance with claim 1 comprising 1-99 percent gold flake and 99-1 percent of a finely divided inorganic binder. 